Merge pull request #170 from dsrao711/issue_169

Python solution for Post order reversal, iterative and recursive

Author: smv1999

DSA 450 GFG/post-ord-iterative.py

@@ -0,0 +1,38 @@
+
+# https://leetcode.com/problems/binary-tree-postorder-traversal/
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def postorderTraversal(self, root: TreeNode) -> List[int]:
+      
+      if root == None:
+        return
+      
+      stack = deque()
+      stack.append(root)
+
+      # create another stack to store postorder traversal
+      out = deque()
+
+      # loop till stack is empty
+      while stack:
+
+          # pop a node from the stack and push the data into the output stack
+          curr = stack.pop()
+          out.append(curr.val)
+
+          # push the left and right child of the popped node into the stack
+          if curr.left:
+              stack.append(curr.left)
+
+          if curr.right:
+              stack.append(curr.right)
+              
+      out.reverse()
+      
+      return out

DSA 450 GFG/post-order-rec.py

@@ -0,0 +1,50 @@
+#https://www.hackerrank.com/challenges/tree-postorder-traversal/problem
+
+class Node:
+    def __init__(self, info): 
+        self.info = info  
+        self.left = None  
+        self.right = None 
+        self.level = None 
+
+    def __str__(self):
+        return str(self.info) 
+
+class BinarySearchTree:
+    def __init__(self): 
+        self.root = None
+
+    def create(self, val):  
+        if self.root == None:
+            self.root = Node(val)
+        else:
+            current = self.root
+         
+            while True:
+                if val < current.info:
+                    if current.left:
+                        current = current.left
+                    else:
+                        current.left = Node(val)
+                        break
+                elif val > current.info:
+                    if current.right:
+                        current = current.right
+                    else:
+                        current.right = Node(val)
+                        break
+                else:
+                    break
+
+"""
+Node is defined as
+self.left (the left child of the node)
+self.right (the right child of the node)
+self.info (the value of the node)
+"""
+def postOrder(root):
+    #Write your code here
+    if root : 
+      postOrder(root.left)
+      postOrder(root.right)
+      print(str(root.info) + " " , end = "")